1. Filed of the Invention
The present invention relates to an ultrasonic beam forming system, and more particularly to a system for effecting simultaneous multi-directional reception and dynamic focussing while employing only a single delay line.
2. Description of the Related Art
An ultrasonic wave is focused in the following way. Each of a plurality of transducers arranged on the surface of an ultrasonic probe, is operated to convert a received ultrasonic wave signal into an electric signal. The electric signal from each transducer is amplified by a receiving amplifier, corresponding to each transducer, and fed into the delay line alloted to each transducer. The delay time of each delay line is adjusted to regulate focussing so that the signals reflected from a specified point of a human body, as received by each transducer, are output at the same time from the respective output terminals of the corresponding delay lines.
FIG. 1 shows a mode of a fixed focussing system in a conventional ultrasonic wave reception device. Reference numeral 1 in FIG. 1 denotes an ultrasonic probe, 2-i respective transducers, 3-i delay lines, T-i terminals and A an ultrasonic wave reflection point, or target In this figure, receiving amplifiers are not depicted.
The ultrasonic wave signal reflected from the point A is received by the transducers 2-i and each of said transducers 2-i converts the wave signal to an electric signal.
In this case, since the respective distances from the transducer 2-1 and the transducer 2-4, for example, to point A are different, the delay line 3-i is disposed for the transducer 2-i in order to correct for this distance difference. In other words, the difference of the distance is corrected so that ultrasonic emitted from the point A at the same time, are received and converted by the respective transducers 2-i, and appear simultaneously at each terminal T-i.
In the case of the system shown in FIG. 1, the delay time in the above-noted delay lines 3-i must be adjusted again whenever the position of the ultrasonic wave reflection point A becomes different i.e., changes.
FIGS. 2 and 3 show two different types of structures for the delay line shown in FIG. 1. In the drawings, reference numerals 3 and 3-i denote the delay line, and reference numeral 4 denotes a multiplexer. Symbol T-i denotes a terminal that corresponds to the terminal shown in FIG. 1.
In the case of FIG. 2, one delay line 3-i is provided for each channel (i.e., the channel corresponding to each transducer 2-i) shown in FIG. 1, and the delay time described above is adjusted, in principle, by a multiplexer 4.
In the case of FIG. 3, a single delay line 3 equipped with taps is provided for a plurality of channels, and the terminals 2-i and T-i, shown in FIG. 1 and corresponding to the respective channels, are connected to the multiplexer 4. The multiplexer 4 is constituted such that the signal connected to the terminal on the input side can be changeably connected (i.e., selectively switched) to each terminal on the output side. For example, the connection state described above is switched and set, depending on which input terminal should be guided to any particular transducer output. In other words, the delay time described above is decided in advance correctly, and a desired delay time is given to the signal from each channel at the output terminal of the delay line. The signals are then added together.
When a signal on any ultrasonic scanning line is received, the focus must be changed every moment from a short distance to a long distance. Therefore, the delay time of each delay line in FIG. 1 must be changed dynamically. It is necessary to change over a multiplexer dynamically in order to carry out such change in FIG. 2 or FIG. 3. Nevertheless, when a multiplexer is switched, a switching noise is produced to an extent which can not be neglected in comparison with level of signal passing through the multiplexer. Two typical methods are known which can solve these problems.
FIG. 4 shows an example of a two-route alternate switching system. Reference numerals 2-i, 3-i and letter A in FIG. 4 identify the same elements as in FIG. 1. Reference numeral 5-i denotes amplifiers, 6A and 6B delay line units for subsequent reflection points #1 and #2, 7A and 7B denote adders, 8 is a selector switch, and B and C denote other reflection points.
To accomplish the dynamic focussing described above, the delay lines 3-i shown in FIG. 1 are sequentially and simultaneously changed over as the position of the reflection point becomes different, (i.e., changes) in a manner so as to attain the corresponding delay times, respectively.
However, in this switching operation, a switching noise generally occurs. Therefore, in the system shown in FIG. 4, the units 6A and 6B are separately disposed so that while the unit 6A is adjusted so as to detect the ultrasonic wave signal from the refection point A or in other words, while the switch 8 is connected to the unit 6A side, the delay lines 3-i 2 are together (i.e., simultaneously adjusted in the unit 6B so that the ultrasonic wave signal from the reflection point B can be detected next in the unit 6B. While this unit 6B thereafter detects the ultrasonic wave signal from the reflection point B, the delay lines 3-i l in the unit 6A are together (i.e., simultaneously) adjusted so that the ultrasonic wave signal from the reflection point C can be detected next in the unit 6A.
This procedure reduces the serious influence of the switching noise generated at the switch 8, because the signal passing through the switch 8 is large enough due to the signal addition at the adder 7A or 7B in FIG. 4.
One of the problems in the case of the two-system alternate switching system shown in FIG. 4 is that two systems of respective delay line groups are necessary.
FIG. 5 shows an example of the case of a phase control system (Refer to U.S. Pat. No. 4,140,022). Reference numerals 2-i, 3, 5-i and A in the drawing correspond to those used in FIGS. 1, 3 and 4, respectively. Reference numeral 9-i denotes a signal waveform.
In the case of the system shown in FIG. 1, the difference of the distance from the reflection point A is corrected by the delay lines 3-i. However, it is possible to resolve that the focus is adjusted to the reflection point A, if the positive peak point of the alternating signal appearing, for example, at the terminal T-1 in FIG. 1, can be synthesized so as to superpose with the positive peak points of the respective alternating signals appearing at the terminals T-2, T-3, . . . , even though the correction for eliminating the difference of the distance described above is not made.
The phase control system shown in FIG. 5 utilizes this principle. In other words, the difference of the time t exists, between the signal 9-1 from the transducer 2-1 and the signal 9-p from the transducer 2-p, at the start as shown in the drawing. For this reason, the positive peak point of the signal 9-1 does not always coincide with the positive peak point of the signal 9-p and may come to have an opposite phase, or as the case may be.
The phase control system shown in FIG. 5 is provided with a means for adjusting the phase of the signal 9-p, for example, and bringing it into conformity with the phase of the signal 9-1, though said means is omitted from FIG. 5.
FIG. 6 shows the operation of the phase adjustment means. Reference numeral 10 denotes a multiplier. It will be hereby assumed that EQU cos(.omega.t+.phi.)
is supplied as the input signal, and EQU cos(.alpha.t+.theta.)
is supplied as the reference signal. In this case, the output signal of the multiplier 10 is given as follows: EQU 1/2[cos{(.omega.+.alpha.)t+.phi.+.theta.}+cos{.omega.-.alpha.)t+.omega.-.th eta.]
When a filter is applied in a manner so as to extract a component having a frequency (.omega.-.alpha.)/2.pi., for example, from the output signal of the multiplier 10, this after-multiplication channel signal is given by EQU cos{({.omega.-.alpha.)t+.phi.-.theta.}.
It can thus be appreciated that the phase of the after-multiplication channel signal can be changed by adjusting the phase .theta. in the reference signal.
In the case of the phase control system shown in FIG. 5, the phase adjustment on the basis of the principle shown in FIG. 6 is applied to the signal 9-p, for example, so that its positive peak may be in conformity with that of the signal 9-1.
As described above, these two systems are known as dynamic focussing.
On the other hand, in the ultrasonic diagnosis, the affected parts are scanned while the ultrasonic wave is generated, and the reflected wave is received. In this case, the diagnosis is carried out by transmitting the ultrasonic wave in a certain direction, receiving the reflected wave, transmitting the ultrasonic wave in the next direction to receive a reflected wave, and repeating these procedures. Therefore, the scanning time is made longer.
A simultaneous multi-directional reception system has been known in the past in order to improve this problem.
FIG. 12 shows a typical simultaneous multi-directional reception system. After the outputs of the transducers are amplified, the outputs of direction "1" are summed up, by an adder 104-1 to create a final output for a direction "1", whereas outputs of direction "2" are summed up by an adder 104-2 to create a final output for a direction "2".
FIG. 7 shows the operation of the simultaneous multi-directional reception system, and FIG. 8 is a view showing sound pressure vs. direction characteristics in FIG. 7. Reference numerals 2-i, 5-i, Ai and Bi correspond to those used in FIG. 1, etc. Reference numeral 11 denotes a transmission direction of the ultrasonic wave, 12-1 and 12-2 are reception directions, and 13-1 and 13-2 are focussing units, respectively.
In the case of the simultaneous multi-directional reception system shown in FIG. 7, the ultrasonic wave is transmitted in the direction represented by reference numeral 11, a first direction focussing unit 13-1 is so set as to receive a reflection from a point Al in the direction 12-1 and a second direction focussing unit 13-2 is set so as to receive a reflection from a point A2 in the direction 12-2 shown in the drawing. Needless to say, it can be understood that dynamic focussing is effected in the respective focussing units 13-i in a manner so as to receive the reflection from the point B1 or B2 in the same direction.
FIG. 8 is a drawing explaining the principle of the simultaneous multi-directional reception. Reference numeral 14 in FIG. 8 denotes transmission directivity characteristics in the direction 11, reference numeral 15-1 reception directivity characteristics in the return direction 12-1 and reference numeral 15-2 reception directivity characteristics in the return direction 12-2.
When the directivity characteristics described above are characteristics 14 and 15-1 as shown, respectively, the directivity characteristics of the signal received by the transducer 2-i become the overall reception characteristics as represented by reference numeral 16-i in FIG. 8. It is possible to consider that the first direction focussing unit 13-1 and the second direction focussing unit 13-2 are arranged in a manner so as to match the characteristics 16-1 and 16-2 shown in the drawing, respectively.
The following can be noted when the hardware quantities (particularly the numbers of the delay lines) are compared with one another between the fixed focus system shown in FIG. 1, the two-route alternate switching system shown in FIG. 4 and the phase control system shown in FIG. 5. In other words, when the quantity of the system shown in FIG. 1 is assumed to be "1", the quantity of the system shown in FIG. 4 is "2" and the quantity of the system shown in FIG. 5 is "1".
Furthermore, the following can be noted in the simultaneous multi-directional reception system shown in FIG. 7:
(1) The hardware quantity described above is "2" when the fixed focussing is employed.
(2) The above quantity is "4" when the two-route alternate switching system is employed.
(3) The above quantity is "2" when the phase control system is employed.
From the above, the above quantity becomes "2" even when the phase control system is employed, if the simultaneous multi-directional reception system is used after accomplishing dynamic focussing.
In accordance with the present invention, even only one (i.e., a single) route beam former can perform dynamic focussing and further, a simultaneous multi-directional reception can be effected.